Disc drives are digital data storage devices that store and retrieve large amounts of user data in a fast and efficient manner. The data are magnetically recorded on the surfaces of one or more rigid data storage discs affixed to a spindle motor for rotation at a constant high speed. The discs and spindle motor are commonly referred to as a disc stack.
The disc stack is accessed by an array of vertically aligned data transducer heads that are controllably positioned by an actuator assembly. Each head typically includes electromagnetic transducer read and write elements that are carried on a fluid bearing slider. The fluid can be air or alternatively a fluid such as helium. The slider acts in a cooperative hydrodynamic relationship with a thin layer of fluid dragged along by the spinning discs to fly each head in a closely spaced relationship to the disc surface.
In order to maintain the proper flying relationship between the heads and the discs, the heads are attached to and supported by flexible suspension assemblies, also called flexures. An actuator motor, typically a voice coil motor (VCM), rotates the actuator assembly to cause the heads to move across the disc recording surfaces. The actuator assembly is also referred to as a head stack assembly (HSA). Both the disc stack and the head stack assembly are mounted to and supported by a rigid base deck of the drive.
Disc drives are typically manufactured using high volume automated assembly lines. In a typical automated line, the drives are assembled on pallets conveyed to various assembly stations, each station adding a different set of components to, or performing a different operation on, the drives.
One such station commonly found in a typical automated assembly line is a head disc merge station in which a head stack assembly is merged with a disc stack. The term “merge” in this context refers to the insertion and positioning of the heads into the disc stack, that is, positioning the heads between and adjacent to the discs in their final assembled relationship.
In some merge stations, following the merging of the head stack assembly and the disc stack, the merged head stack assembly and disc stack are together mounted to the base deck. In other merge stations, the sequence of assembly is to mount the disc stack to the base deck; mount the head stack assembly to the base deck with the heads at a position outside the outermost diameter of the disc stack; and rotate the head stack assembly to merge the heads into the disc stack.
Typically, at the conclusion of a merge operation, the heads are positioned near an innermost diameter of the disc stack, resting against textured landing zones on the disc surfaces. The landing zones provide reduced stiction between the heads and discs to allow the heads to safely park during non-operation of the drive.
A latching arrangement secures the head stack assembly when the heads are parked to prevent the heads from inadvertently contacting the data recording surfaces in response to the application of a mechanical shock to the drive, as allowing the heads to contact the data recording surfaces when the discs are not rotating can damage the drive.
It is thus necessary to support the heads above the respective disc surfaces during the merge operation as the heads are positioned in the final park position. Some have proposed applying power to the spindle motor to rotate the discs and powering the actuator motor so that the heads are supported by disc rotation fluid bearings during the merge operation. Usually, however, the merge operation is performed with stationary discs and while the heads are supported as the heads are advanced to the park position.
Head stack assemblies are typically purchased from a head stack assembly manufacturer and are provided with removable shipping spacers. The shipping spacers are comb-like structures that support the flexures to protect the heads from inadvertent contact with each other and prevent deformation of the flexures during shipping and handling.
During a typical merge operation, a merge comb, or merge spreader, is inserted into the head stack assembly at the merge station to provide appropriate spacing between the heads. The spacer comb is removed once the merge comb engages the flexures, and the heads are advanced to the final park position.
Usually, the merge comb supports the flexures and the heads as the heads are moved from the outermost diameter of the discs to the innermost diameter of the discs in such a manner that contact is prevented between the disc stack and either the merge comb or head stack assembly until the merge comb releases the heads in the final park position. Once the heads are parked, the merge comb is retracted and the merge operation cycle is completed.
The merge combs can become bent or otherwise damaged. Thus, it has been necessary to implement an inspection routine to minimize or avoid the damage that occurs with unwanted contact between the merge comb and the disc stack. Otherwise, expensive rework or component replacement is risked.
Some merge comb inspection methods include go/no go gages applied by an assembly operator prior to the merge operation cycle. This is time consuming, as well as being subjective to operator judgment. Another merge comb inspection method is that of removing the merge comb from the merge station and subjecting the merge comb to traditional inspection routines. Again, however, this latter mentioned merge inspection method is time consuming. Any improved quality from the methods comes at the cost of reduced production rates.
There is therefore a continuing need for an accurate and fast method and apparatus to inspect a head disc merge comb to avoid damage to disc stacks, and to address other limitations associated with the current state of the art.